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  • 1
    Electronic Resource
    Electronic Resource
    Restricted rotation about partial C,N double bonds (1997)
    Springer
    Structural chemistry 8 (1997), S. 217-226 
    Details
    ISSN: 1572-9001
    Keywords: NMR ; ab initio calculation ; restricted rotation ; solvent effects ; NBO
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The restricted rotation about the partial C,N double bond in 2-chloro-6-NR2-pyran-4-ones is discussed in the light of NMR spectroscopic data and theoretical calculations.Ab initio calculations at the HF/6-31G* level were carried out using a continuum model to take solvent effects into account. The delocalization ofπ-electron density [described by natural bond orbital analysis (NBO)] was applied to determine the degree of conjugation in the ground state (GS) and in the transition state (TS) for the restricted rotation of the compounds studied. The reason for the different barriers to rotation of the NR2 substituents (pyrrolidino 〉 dimethylamino 〉 morpholidino 〉 piperidino) at the 2-chloro-pyran-4-one ring appears to be the different steric hindrance of the NR2 substituents in the GS for the restricted rotation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02263510
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  • 2
    Electronic Resource
    Electronic Resource
    Acyclic stereochemical analysis by NMR spectroscopy (1987)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 25 (1987), S. 990-995 
    Details
    ISSN: 0749-1581
    Keywords: NMR ; γ-chloropropyl methyl ethers ; Vicinal H,H coupling constants ; Steric compression Conformation ; Diastereomer assignment ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The diastereomers of a series of substituted γ-chloropropyl methyl ethers with up to three chiral centres have been assigned by 1H/13C NMR spectroscopy from vicinal H,H coupling constants and the steric compression within the carbon skeleton (γ-gauche effect). The necessary conformational study was carried out with the help of theoretically estimated steric 1,3-parallel interaction energies.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260251114
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  • 3
    Electronic Resource
    Electronic Resource
    Stereochemistry of crown ethers. V.For Part 4, see S. Stoss, E. Kleinpeter and H.-J. Holdt, Magn. Reson. Chem. 29, 999 (1991). - solution structure and complexational behaviour of dibenzo crown ethers (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 425-433 
    Details
    ISSN: 0749-1581
    Keywords: Dibenzo crown ethers ; Conformations ; NMR ; Molecular mechanics ; Alkali complexes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preferred conformations and the complexing behaviour of 16- and 17-membered dibenzo crown ethers were studied by means of both NMR spectroscopy and molecular mechanical calculations. Conclusions could be drawn about the stoichiometry and stability of the alkali metal ion corand complexes. The spin-lattice relaxation times of the crown ether carbon atoms and the relevant complexes are discussed with respect to the intramolecular flexibility of these species. The intramolecular reorientations detected are reduced considerably in the alkali metal ion complexes. In the preferred conformers of corands 2, 3 and 6, the molecular mechanical calculations prove that the phenyl rings are positioned in a chair conformation at a twist to each other. The same phenyl rings in the crown ethers 1, 4 and 5 are in a boat conformation. These conformations seem to be important for the optimum complexation of the alkali cations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260300514
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  • 4
    Electronic Resource
    Electronic Resource
    Conformational study of the 4,9-dihetero-(Z,Z)-cyclodeca-1,6-diene ring system; the mono- and di-benzo analogues (1990)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 28 (1990), S. 628-634 
    Details
    ISSN: 0749-1581
    Keywords: 13C NMR ; 1H NMR ; 4,9-Dihetero-(Z,Z)-cyclodeca-1,6-dienes ; Ring inversion barriers ; Restricted rotation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dynamic 1H and 13C NMR spectra of a series of mono- and bis-annelated 4,9-dihetero-(Z,Z)-cyclodeca-1,6-dienes were obtained and are discussed with respect to ground-state conformers and the barriers to ring inversion, and to the restricted rotation about exocyclic partial C,N double bonds. The ten-membered rings are, with one exception, anancomeric chair conformers and interconvert via a combination of single bond rotations and bond angle bendings. Depending on the heteroatoms present, the series of decreasing barriers to ring inversion S 〉 NH 〉 O was obtained. Benzannelation decreases the free energy of activation of the same dynamic process owing to greater intramolecular transannular H,H interactions.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260280713
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  • 5
    Electronic Resource
    Electronic Resource
    Study of the distribution of the π-electrons in push-pull alkenes by 1H and 13C NMR spectroscopy (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 212-222 
    Details
    ISSN: 0749-1581
    Keywords: Dynamic NMR ; 13C NMR ; Push-pull alkenes ; Restricted C,C and C,N rotation ; π-Electron density distribution ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Push-pull alkenes with variable structure were investigated with respect to the influence of the different substituents at the central C,C double bond on the dynamic behaviour of this type of compound. 1H and 13C NMR spectroscopic investigations were carried out for ketene-S,S-, -S,N- and -N,N-acetals. HMO calculations were employed to discuss the related π-electron density distributions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260290305
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  • 6
    Electronic Resource
    Electronic Resource
    Restricted rotations about exocyclic partial double bonds. The electronic state of heteroaromatic six-membered rings (1987)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 25 (1987), S. 688-695 
    Details
    ISSN: 0749-1581
    Keywords: 13C NMR ; Temperature dependent ; 1HNMR spectra ; Pyrylium/thiopyrylium salts ; Pyrones/thiopyrones ; Rotational barriers ; Partial double bond character ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Temperature-dependent 13C and 1H NMR spectra of three series of six-membered heteroaromatic systems with NR2 substituents attached to pyrylium/thiopyrylium salts and pyrones/thiopyrones have been recorded. The rotational barriers thus determined about the exocyclic partial double bonds are discussed in terms of dominating mesomeric structures, in order to describe the electronic state and the spatial conditions in the molecular framework. Cyanine and merocyanine substructures have been identified by NMR and express the electronic state predominantly present in the compounds.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260250807
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  • 7
    Electronic Resource
    Electronic Resource
    d-NMR-Untersuchungen der behinderten Rotation am N—C-(X)-Bindungsinkrement. VIII. Metallkomplexverbindungen von 1,1-Diäthyl-3-benzoylthio- und selenoharnstoffVII. Mitteilung: E. Kleinpeter, R. Widera u. M. Mühlstädt, Z. Chem., 17, 298 (1977). (1977)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 437 (1977), S. 282-288 
    Details
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: d-N.M.R. Studies of Hindered Rotation on N—C(X) Bond Increment. VIII. Metal Complexes of 1,1-Diethyl-3-benzoylthio- and selenoureaThe coordination of 1,1-Diethyl-3-benzoylthiourea (debtu) and 1,1-Diethyl-3-benzoylselenourea (debsu) to a metal ion leads both with subgroup elements (Ni(II), Pd(II), Co(III), Zn(II), Cu(I)) and with main group elements (Pb(II), Tl(I)) to an increase of the free enthalpy of activation of the rotational process about the terminal N—C(X) bond. The order of the increase is with debtu: Ni(II) 〉 Pb(II) 〉 Pd(II) 〉 Co(III) 〉 Tl(I) and with debsu: Ni(II) 〉 Zn(II) 〉 Pd(II) 〉 Co(III). A decrease of the barrier of rotation was observed with Tl(debsu) only, which is dimeric in benzene solution. The characteristic IR-data of the ligand debtu and its Pd(II)-, Ni(II)-, and Tl(I)-complexes, and of the Cu(debtu)3Cl complex are given. The results are discussed.
    Notes: Die Koordination der Liganden 1,1-Diäthyl-3-benzoylthioharnstoff (debtu) und 1,1-Diäthyl-3-benzoylselenoharnstoff (debsu) an ein Metallatom führt sowohl bei Nebengruppenelementen (Ni(II), Pd(II), Co(III), Zn(II), Cu(I)) als auch bei Hauptgruppenelementen (Pb(II), Tl(I)) zur Erhöhung der freien Aktivierungsenthalpie ΔGc≠ der Rotation um die N—C(X)-Bindung. Die Reihenfolge der Erhöhung ist beim debtu: Ni(II) 〉 Pb(II) 〉 Pd(II) 〉 Co(III) 〉 Tl(I) und beim debsu: Ni(II) 〉 Zn(II) 〉 Pd(II) 〉 Co(III). Nur beim Tl(debsu) beobachtet man eine Erniedrigung der Rotationsbarriere. Es liegt in benzolischer Lösung dimer vor. Die charakteristischen IR-Daten des Liganden debtu und seiner Pd(II)-, Ni(II)- und Tl(I)-Komplexe, sowie die des Cu(debtu)3Cl werden angegeben. Die erhaltenen Ergebnisse werden diskutiert.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19774370141
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  • 8
    Electronic Resource
    Electronic Resource
    Dynamische NMR-Untersuchungen der behinderten Rotation am N—C(X)-Bindungsfragment. XVIIXVI. Mitteilung: E. Kleinpeter und D. Thomzik, J. prakt. Chem., im Druck.. Einfluß des Zentralmetallatoms auf die Rotationsbarriere der behinderten C, N-Rotation und die 13C-NMR-Spektren von Chelatkomplexen des 1,1-Diethyl-3-benzoyl-thio(seleno)-harnstoffs (1982)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 495 (1982), S. 105-114 
    Details
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Dynamic N.M.R. Studies of Hindered Rotation on N—C(X) Bond Increment. XVI. Central Metal Atom Influence on Rotational Barriers of the Restricted C, N-Rotation and the 13C N.M.R. Spectra of the Metal Complexes of 1,1-Diethyl-3-benzoyl-thio(seleno) UreaThe rotational barriers about the partial C, N-double bond Et2N—C(X) in the metal complexes of 1,1-diethyl-3-benzoyl-thio(seleno) urea are submitted, corrected for the compounds of low Δν value. The barriers are dependent on the electric polarizibility of the metal ion and the chalcogen atom X (S, Se). The results are discussed. In the 13C n.m.r. spectra of the investigated compounds also the most electron attractive metal ions influence characteristic variations of 13C chemical shifts.
    Notes: Die Rotationsbarrieren um die partielle C, N-Doppelbindung Et2N—C(X) in den Metallchelaten des 1,1-Diethyl-3-benzoyl-thio(seleno)-harnstoffs (M = NiII, PdII, PtII, ZnII, PbII, CuI und TlI) werden berichtet und für die Verbindungen mit niedrigen Δν-Werten (〈 8 Hz) korrigiert. Die bestimmten ΔGc≠-Werte sind von der mittleren elektrischen Polarisierbarkeit des Metallatoms und der Art des Chalkogenatoms X (S, Se) abhängig. Die erhaltenen Ergebnisse werden diskutiert. In den 13C-NMR-Spektren werden die Liganden-C-Atome durch die Komplexierung mit den Metallionen abhängig von deren elektronenziehendem Charakter unterschiedlich beeinflußt.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19824950110
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  • 9
    Electronic Resource
    Electronic Resource
    M1P(SiMe3)2 (M1 = Li, Na, K) - Ein Baustein zur Synthese von iso-Tetraphosphanen des Typs P(PR2)3 (R = Ph, cyclo-C6H11(Cy))Professor Helmut Köhler in memoriam (1991)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 600 (1991), S. 203-210 
    Details
    ISSN: 0044-2313
    Keywords: Alkali metal-bis(trimethylsilyl) phosphides ; iso-tetraphosphines ; (P—P)-bond formation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: M1P(SiMe3)2 (M1 = Li, Na, K) - A Building Unit for iso-Tetraphosphines of the Type P(PR2)3 (R = Ph, cyclo-C6H11(Cy))M1P(SiMe3)2 (M1 = Li, Na, K) reacts with diorganochlorophosphines to form iso-tetra-phosphines of the type P(PR2)3 (R = Ph, Cy). The reaction follows a stepwise pathway via di- and tri-phosphines as shown by 31P-NMR. In the case of tBu2PCl the reaction stops on the step of the triphosphine (tBu2P)2PH. The reactivity of the alkali phosphides M1P(SiMe3)2 decreases in the sequence K 〉 Na 〉 Li.
    Notes: Die Reaktion von M1P(SiMe3)2 (M1 = Li, Na, K) mit Diorganochlorphosphanen führt zur Bildung der iso-Tetraphosphane des Typs P(PR2)3 (R = Ph, Cy). 31P-NMR-spektroskopisch konnte der stufenweise Aufbau über Di- und Triphosphane als Zwischenprodukte nachgewiesen werden. Für t-Bu2PCl bleibt die Reaktion aus sterischen Gründen auf der Stufe des Triphosphans (t-Bu2P)2PH stehen. Es zeigt sich folgende Abstufung in der Reaktivität der Alkaliphosphide M1P(SiMe3)2: K 〉 Na 〉 Li.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19916000128
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